External users cannot open encrypted email

Sorry if this is somewhat off the beaten path.    Perhaps it is a piece of the puzzle.I use Microsoft 365 for Family.   So,...it is indeed M365.

Using Outlook on the Web (OWA).

It offers the Encrypt function when sending a new email.

When I send to an M365-Family recipient, and/or an "Outlook.com personal account", the recipient can open and read the Encrypted email.    Recipient using OWA on Chrome.   Recipient sees a Lock icon in the Inbox list, and when message is open shows message--  This message is encrypted. 

So...it works OK.

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However, the same email, sent to a recipient using Google gmail.com, cannot read the email.

The gmail recipient receives the email.

   (note-- always seems to be delayed about 10 minutes).

Sees:   --- has sent you a protected message.     A blue box with --Read the message--.

When the recipient clicks on that blue box,  sees this:

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Sorry, we can't display your message right nowSomething went wrong and your encrypted message couldn't be opened.Please try again by following the instructions in the original email message in 5 minutes.

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With  M365 Family  I probably do not have any "Exchange system admin" tools.

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Note:  a few months ago, this did indeed work correctly.   The Gmail recipient was asked to Logon with an account or receive a one-time code.   The recipient used the one-time code, and then was able to read the encrypted email.

Thanks.

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